Method of driving liquid-drop spraying device

ABSTRACT

A liquid-drop spraying device is provided which can perform a stable liquid discharge without producing air bubbles in the liquid of the pressurized room as well as the amount of liquid supply per unit time is increased. The liquid can be flowed into the pressurized room uniformly and without entrainment of bubbles from the nozzle side by making an initial discharge (or charge) time constant larger than a subsequent discharge (or charge) time constant, which in turn allows liquid in the pressurized room to be replaced by slow suction followed by fast suction.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of driving a liquid-dropspraying device for use in various kinds of machines for processing theabove described liquid-drop by means of discharging the liquid-drop. Thepresent invention is particularly useful as a liquid discharging deviceupon drying process of various liquid raw materials which are requiredfor stable liquid discharges, and is preferable as a discharging devicefor various liquid, such as a liquid discharging device upon drying asolution including product aiming at supplying reactive raw materialssuch as pharmaceutical synthesis and powder production.

2. Description of the Prior Art

As for a conventional method of driving a liquid-drop spraying device,in a driving device for a liquid-drop spraying device comprising aplurality of minimal liquid-drop discharge units having respectivelypressure means for discharging a liquid, a pressurized room forpressurizing discharge liquid, a nozzle for liquid discharge connectedto the pressurized room, an inlet hole for supplying a liquid into thepressurized room, the foregoing inlet holes for supplying liquid of aplurality of liquid drop discharge units adjacent to each other beingconnected through a common liquid supplying path, and having therelevant piezoelectric\electrostriction element in a portion of a wallportion of the relevant liquid pressurized room, there has been aconventional method of driving a liquid-drop spraying device, in whichthe wall portion of the relevant liquid pressurized room is deformed byapplying a predetermined voltage signal (charging or discharging) to therelevant piezoelectric\electrostriction element, hence, a liquidsupplied to the relevant liquid pressurized room is sprayed from theforegoing nozzle by the pressure produced in the relevant liquidpressurized room, and a liquid is supplied from the inlet hole to thepressurized room by recovering the distortion of the relevant liquidpressurized room to the original form.

Then, depending upon a kind of liquid drop processing device mounted ona liquid drop spraying device, there is a device for use in supplying alarge amount of liquid, a large amount of liquid is supplied byenlarging aperture of a nozzle hole and inlet hole.

However, in the case where an aperture of a nozzle hole is made toolarge, discharging liquid cannot be a minimal liquid-drop. Neither, asfor an inlet hole, since an inlet hole not only has a function as a paththrough which the liquid is supplied into the pressurized room, but alsohas a function preventing back flow even if pressurized at the time whena liquid is sprayed from nozzle hole, the aperture of the hole cannot bewidened to unlimited. Therefore, although the number of times ofapplication per unit time period is increased and an amount of supplyingvolume of liquid is increased by shortening an interval time period ofapplying a predetermined voltage signal topiezoelectric\electrostriction element, since liquid supply from aninlet hole to a pressurized room is delayed, it cannot be carried out tostably supply a larger amount of the liquid.

DISCLOSURE OF THE INVENTION

As for a method of driving a liquid-drop spraying device according tothe present invention, in a liquid-drop spraying device comprising aplurality of minimal liquid-drop discharge units respectively having anozzle for liquid discharge, a pressurized room for pressurizing aliquid made discharge from the relevant nozzle, an inlet hole supplyinga liquid into the relevant pressurized room andpiezoelectric\electrostriction element making the relevant pressurizedroom pressurize and operate, the foregoing liquid inlet holes of aplurality of liquid-drop discharge units being connected to a commonliquid supplying path, a method of driving a liquid-drop spraying deviceaccording to the present invention is provided, in which a wall portionof the foregoing pressurized room is deformed by repeatedly applying apredetermined voltage signal to the foregoingpiezoelectric\electrostriction element, thereby spraying a liquidsupplied into the relevant pressurized room from the foregoing nozzle bythe pressure produced in the pressurized room, characterized in that theratio of the foregoing inlet hole aperture to the foregoing nozzle holeaperture (inlet hole aperture/nozzle hole aperture) ranges from equal toor more than 0.6 to equal to or less than 1.6, and the ratio of thenozzle hole aperture and the nozzle thickness (nozzle holeaperture/nozzle thickness) ranges from equal to or more than 0.2 toequal to or less than 4, after the foregoing applying voltage signalsupplies and charges the current from starting charge voltage to theforegoing piezoelectric\electrostriction element, retaining final chargevoltage during certain time period, and then discharges having more than2 kinds of discharge time constants are in turn performed, and theinitial first discharge time constant is larger than the next seconddischarge time constant, making the foregoing starting charge voltage asa reference, the second discharge is started with voltage ranges fromequal to or more than 35% to equal to or less than 70% of voltagedifference between the foregoing starting charge voltage and theforegoing final charge voltage.

The present invention effectively acts when discharging on a liquidhaving a low viscosity, concretely, a liquid having a viscosity of 0.2mPa/S-30 mPa·S, preferably a liquid having a viscosity of 0.5 mPa/S-1.2mPa/S, in the case where liquid-drops are discharged from a plurality ofliquid-drop discharge units at the same time according to the abovedescribed constitution, when a liquid is supplied from a liquid inlethole into a liquid pressurized room after liquid discharge, since itperforms rapidly suctioning the liquid having started to move than atthe first suction speed and smoothly supplying the liquid and in a shorttime into the liquid pressurized room after first comparatively slowlysuctioning the liquid and flowing the liquid into the whole inlet holes,a stable discharge of liquid can be carried out without producingbubbles in the liquid of the liquid pressurized room as well as anamount of liquid supplying per unit time period is increased.

Moreover, rapid pressure variation within pressurized room is avoided byretaining final charge voltage during certain time period immediatelyafter discharging liquid-drop and that bubbles entering into apressurized room from a nozzle by vibration of liquid level in a nozzlefor liquid discharge is avoided, but immediately after startingdischarge voltage, liquid vibration in a nozzle for liquid discharge isstill remained. Hence, during the foregoing vibration is remained,discharge time constant is made larger, then suctioning the liquid byslow pressure variation, consequently when the foregoing vibration hasbeen attenuated, if discharge is rapidly performed at the seconddischarge time constant, entrainment of bubbles from the nozzle forliquid discharge into the pressurized room by pressure variation ofdischarge time can be prevented, time interval of applying apredetermined voltage signal can be shortened topiezoelectric\electrostriction element and an amount of liquid supplycan be increased since discharge at the second discharge time constantis rapidly performed.

Furthermore, voltage starting discharge at the second discharge timeconstant is preferably made ranged from equal to or more than 35% toequal to or less than 70% of voltage difference between starting chargevoltage and final charge voltage, making starting discharge voltage as areference.

When the starting discharge voltage is equal to or less than 35%, sincedischarge whose discharge time constant is large, i.e., suction which isslowly performed occupies most of all suctioning steps, suction itselfis securely performed, however, an amount of suction per unit timeperiod is not taken large, since a discharge period cannot be shortenedas a result, a large amount of discharge cannot be secured. Moreover, inthe case where suction time is taken comparatively smaller in thesituations of the range of the first discharge time constant beinglarger than that of the second discharge time constant so as to take alarger amount of suction per unit time period, the starting of suctionis unstable, and incomplete discharge will be occurred. Furthermore,when the second starting discharge voltage is equal to or more than 70%,since discharge whose discharge time constant is large, i.e., the rateof slow suction is too small, starting of liquid suction cannot berapidly performed, an amount of suction of liquid from the liquid inlethole to the liquid pressurized room is decreased, entrainment of bubblesfrom the nozzle for liquid discharge will be occurred and spraying willbe unstable.

Moreover, upon discharging in the foregoing drive waveform, in the casewhere the ratio of the supplying hole aperture to the nozzle holeaperture (inlet hole aperture/nozzle hole aperture) is larger, if thesuction is considered, it will be well-directed, however, since the rateof the pressure upon discharge being escaped to the side of inlet holeaperture is large, discharge power will be insufficient. Moreover, inthe case where it is smaller, since an amount of insufficient supplywith respect to an amount of discharge is occurred, the ratio of theinlet hole aperture to the nozzle hole aperture (inlet holeaperture/nozzle hole aperture) is preferably between 0.6 and 1.6.

Furthermore, the ratio of the nozzle hole aperture to nozzle thickness(nozzle hole aperture/nozzle thickness) preferably ranges from equal toor more than 0.2 to equal to or less than 4, in the case where the ratioof the nozzle hole aperture to the nozzle thickness (nozzle holeaperture/nozzle thickness) is equal to or less than 4, residualvibration of liquid level immediately after liquid discharge can berapidly converged by contact resistance with fluid on the wall ofdischarge hole, furthermore, an invasion of bubbles into the pressurizedroom by pressure variation within pressurized room upon discharge can beprevented, spraying stability can be enhanced, the liquid can bedischarged in a shorter time period as a result, and an amount ofspraying can be increased.

Moreover, in the case where the ratio of the nozzle hole aperture tonozzle thickness (nozzle hole aperture/nozzle thickness) is equal to ormore than 0.2, since the contact resistance with the fluid on the wallof discharge hole is large, the occurrence of incomplete discharge dueto the insufficiency of discharge force is prevented. Furthermore, whenthree of the foregoing ratio of the inlet hole aperture to the nozzlehole aperture, the foregoing ratio of the nozzle hole aperture to thenozzle thickness and the foregoing voltage of the second startingdischarge has been fulfilled simultaneously, incomplete spraying due toan invasion of bubbles is prevented, and a large amount of sprayingcould have been secured.

Moreover, it is preferable that in the above described constitution, atime ranging from the time when piezoelectric\electrostriction elementhas started discharge with the second discharge time constant to thetime when the next predetermined voltage signal is applied (T4), is maderanged from equal to or more than one fourth to equal to or less than 20fold of specific vibration period (T) at the time when a liquid issupplied to the channel path within the structure constituted of anozzle for liquid discharge, a pressurized room for pressurizing aliquid to discharge it from the relevant nozzle, an inlet hole forsupplying a liquid into the relevant pressurized room and apiezoelectric\electrostriction element for making the relevantpressurized room pressurize and operate, and the ratio (T3/T4) of a timedischarging at the first discharge time constant (T3) to the timeranging from the time when discharge has been started at the seconddischarge time constant to the time when the next predetermined voltagesignal is applied to the piezoelectric\electrostriction element (T4) ismade ranged from equal to or more than 0.1 to equal to or less than 20fold.

In the case where the time ranging from the time when thepiezoelectric\electrostriction element has started discharge at thesecond discharge time constant to the time when the next predeterminedvoltage signal is applied (T4) is equal to or less than one fourth ofthe specific vibration period (T), since suction speed of a liquid froma liquid inlet hole into the liquid pressurized room after liquiddischarge is too high, even if the first discharge has started withoutdiscrepancy, the liquid supply from the inlet hole is insufficient intime at the time of suction during the second discharge, an invasion ofbubbles from the nozzle hole for the liquid discharge into thepressurized room makes it incomplete spraying. Moreover, in the casewhere the above described T4 is equal to or more than 20 fold of T,since an amount of suction per unit time period is not taken large,discharge period cannot be shortened as a result and a large amount ofdischarge cannot be secured.

Furthermore, in the case where the ratio of the time discharging at thefirst discharge time constant (T3) to the time ranging from the timewhen discharge has been started at the second time constant to the timewhen the next predetermined voltage signal is applied to thepiezoelectric\electrostriction element (T4) is equal to or less than0.1, since the rate of the first discharge which has a large timeconstant is small, the ratio of an amount of suction of the liquidduring the first discharge with respect to the whole amount of suctionis decreased, suction cannot be sufficient at the time of suction duringthe second discharge and the invasion of bubbles from the nozzle holefor the liquid discharge into the pressurized room may make itincomplete spraying. Moreover, in the case where the above describedratio is equal to or more than 20, since an amount of suction per unittime period is not taken large, discharge period cannot be shortened asa result, and a large amount of discharge cannot be secured.

Moreover, in a form of spraying a liquid-drop during discharge of theforegoing piezoelectric\electrostriction element, the present inventionis a method of driving a liquid-drop spraying device in which a wallportion of a pressurized room is deformed by applying different voltagesignals repeatedly to the piezoelectric\electrostriction element towhich a predetermined voltage signal has been applied, thereby theliquid supplied into the relevant pressurized room is sprayed from theforegoing nozzle by a pressure produced in the pressurized room,characterized in that the ratio of the foregoing inlet hole aperture tothe foregoing nozzle hole aperture (inlet hole aperture/nozzle holeaperture) ranges from equal to or more than 0.6 to equal to or less than1.6, and the ratio of the nozzle hole aperture to the nozzle thickness(nozzle hole aperture/nozzle thickness) ranges from equal to or morethan 0.2 to equal to or less than 4, after the foregoing differentapplying voltage signal has discharged the current from the foregoingpiezoelectric\electrostriction element to which the starting dischargevoltage has been applied, the final discharge voltage during certaintime period is retained, consequently, in turn, charges having equal toor more than two kinds of charge time constants are performed, and thestarting first charge time constant is larger than the next secondcharge time constant, the second charge is started with the voltageranging from equal to or more than 30% to equal to or less than 65% ofthe voltage difference between the foregoing final discharge voltage andthe foregoing starting discharge voltage, and making the foregoing finaldischarge voltage as a reference.

In the case where liquid-drops are discharged simultaneously from aplurality of liquid-drop discharge units according to the abovedescribed constitution, when the liquid is supplied from the liquidinlet hole into the liquid pressurized room following liquid discharge,since after the liquid is first comparatively slowly suctioned and theliquid is flowed into the whole inlet holes, the liquid having startedto move is suctioned rapidly than at the first suction speed and theliquid supply is performed smoothly and in a shorter time into theliquid pressurized room, a stable liquid discharge can be performedwithout making production of any air bubble in the liquid of the liquidpressurized room as well as an amount of the liquid supply per unit timeperiod is increased.

Moreover, although immediately after liquid-drop discharge, abruptpressure variation within the pressurized room is avoided by retainingfinal discharge voltage during certain time period, and entering ofbubbles from the nozzle into the pressurized room due to the vibrationof the liquid level in the nozzle for a liquid discharge is avoided,immediately after starting charge, the vibration of the liquid level inthe nozzle for the liquid discharge remains. Therefore, during theforegoing vibration remains, the charge time constant is made large, theliquid is suctioned with slow pressure variation, consequently, when theforegoing vibration has been attenuated, if charge is rapidly performedwith the second charge time constant, the entrainment of bubbles fromthe nozzle for the liquid discharge into the pressurized room due to thepressure variation during charge can be prevented, and since charge withthe second charge time constant is rapidly performed, a time intervalfor applying a predetermined voltage signal to thepiezoelectric\electrostriction element can be shortened and an amount ofliquid supply can be increased.

Furthermore, it is preferable that the voltage starting charge with thesecond charge time constant is made ranged from equal to or more than30% to equal to or less than 65% of the voltage difference between thefinal discharge voltage and the starting discharge voltage, making thefinal discharge voltage as a reference.

In the case where the starting charge voltage is equal to or more than65%, although the discharge whose discharge time constant is large,i.e., the suction which is slowly performed occupies most of all suctionsteps, the suction itself is securely performed, since an amount ofsuction per unit time period is not taken large, discharge period cannotbe shortened as a result, a large amount of discharge cannot be secured.Moreover, if the suction time is taken comparatively smaller in thesituations of the range of the first charge time constant being largerthan that of the second charge time constant so as to take a largeramount of suction per unit time period, the starting of suction will beunstable and incomplete discharge will be occurred. Moreover, in thecase where it is equal to or less than 30%, since the rate of the chargewhose charge time constant is large, i.e., the suction which is slowlyperformed is too small, the starting of suction of the liquid cannot berapidly performed, an amount of suction from the liquid inlet hole intothe pressurized room following liquid discharge is decreased, andspraying is unstable because the entrainment of bubbles from the nozzlefor the liquid discharge occurs.

Moreover, in the case where discharge is performed in the abovedescribed drive waveform, if the ratio of the supplying hole aperture tothe nozzle hole aperture (inlet hole aperture/nozzle hole aperture) islarger, it will be lead to a good direction in the consideration ofsuction, however, since the rate of the pressure at the discharge beingescaped to the side of inlet hole, discharge force will be insufficient.Moreover, in the case where the ratio is smaller, since theinsufficiency of an amount of supply with respect to an amount ofdischarge is occurred, it is preferable that the ratio of the inlet holeaperture to the nozzle hole aperture (inlet hole aperture/nozzle holeaperture) ranges from equal to or more than 0.6 to equal to or less than1.6.

Furthermore, it is preferable that the ratio of the nozzle hole apertureto the nozzle thickness (nozzle hole aperture/nozzle thickness) rangesfrom equal to or more than 0.2 to equal to less than 4, in the casewhere the ratio of the nozzle hole aperture to the nozzle thickness(nozzle aperture/nozzle thickness) is equal to or less than 4, residualvibration of the liquid level immediately after liquid discharge can berapidly converged by the contact resistance with the fluid on the wallface of discharge hole, furthermore, the invasion of bubbles into thepressurized room due to the pressure variation within the pressurizedroom during charge can be prevented, the spraying stability can beenhanced, discharge can be performed in a shorter time period as aresult, and an amount of spraying can be increased. Moreover, in thecase where the ratio of the nozzle hole aperture to the nozzle thickness(nozzle hole aperture/nozzle thickness) is equal to or more than 0.2,since the contact resistance with the fluid on the wall face of thedischarge hole is large, the occurrence of incomplete discharge due tothe insufficiency of the discharge force can be prevented.

Furthermore, when the three of the above described ratio of inlet holeaperture to the nozzle hole aperture, the ratio of the nozzle holeaperture to the nozzle thickness and the second starting charge voltagehave been fulfilled simultaneously, incomplete spraying due to theinvasion of bubbles can be prevented and a large amount of spraying canbe secured.

Moreover, it is preferable that in the above described constitution, atime ranging from the time when piezoelectric\electrostriction elementhas started discharge at the second discharge time constant to the timewhen the next predetermined voltage signal is applied (T40), is maderanged from equal to or more than one fourth of T to equal to or lessthan 20 T of specific vibration period (T) at the time when a liquid issupplied to the channel path within the structure constituted of anozzle for liquid discharge, a pressurized room for pressurizing aliquid to discharge from the relevant nozzle, an inlet hole supplying aliquid into the relevant pressurized room and apiezoelectric\electrostriction element for making the relevantpressurized room pressurize and operate, and the ratio (T30/T40) of atime for discharging at the first discharge time constant (T30) to thetime ranging from the time when discharge has been started at the seconddischarge time constant to the time when the next predetermined voltagesignal is applied to the piezoelectric\electrostriction element (T40) ismade ranged from equal to or more than 0.1 to equal to or less than 20.

In the case where the time ranging from the time when thepiezoelectric\electrostriction element has started discharge at thesecond discharge time constant to the time when the next predeterminedvoltage signal is applied (T40) is equal to or less than one fourth ofthe specific vibration period (T), since suction speed of a liquid froma liquid inlet hole into the liquid pressurized room after liquiddischarge is too high, even if the first discharge has started withoutdiscrepancy, the liquid supply from the inlet hole is insufficient intime at the time of suction during the second discharge, an invasion ofbubbles from the nozzle hole for the liquid discharge into thepressurized room makes it incomplete spraying. Moreover, in the casewhere the above described T40 is equal to or more than 20 fold of T,since an amount of suction per unit time is not taken large, dischargeperiod cannot be shortened as a result and a large amount of dischargecannot be secured.

Furthermore, in the case where the ratio of the time for dischargingwith the first discharge time constant (T30) to the time ranging fromthe time when discharge has been started at the second time constant tothe time when the next predetermined voltage signal is applied to thepiezoelectric\electrostriction element (T40) is equal to or less than0.1, since the rate of the first discharge which has a large timeconstant is small, the ratio of an amount of suction of the liquidduring the first discharge to the whole amount of suction is decreased,suction cannot be sufficient at the time of suction during the seconddischarge and the invasion of bubbles from the nozzle hole for theliquid discharge into the pressurized room may make it incompletespraying. Moreover, in the case where the above described ratio is equalto or more than 20, since an amount of suction per unit time period isnot taken large, discharge period cannot be shortened as a result, and alarge amount of discharge cannot be secured.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration showing a vertical sectional view in center ofa liquid-drop discharge unit of a liquid-drop spraying device.

FIG. 2 is a graphical representation showing voltage waveform and acontrol signal of a drive electronics of apiezoelectric\electrostriction element along with the passage of time.

FIG. 3 is a diagram of a drive electronics of apiezoelectric\electrostriction element.

FIG. 4 is a graphical representation with measurement data showing astudy of the stability of a liquid-drop spraying device by varying avoltage migrating from discharge using the first discharge time constantto discharge using the second discharge time constant. FIG. 4(a) showsmeasurement data, and FIG. 4(b) is an illustration showing applyingvoltage signals.

FIG. 5 shows another form of a liquid-drop discharge unit, FIG. 5(a) isan illustration showing a vertical sectional view in center, and FIG.5(b) is a sectional view taken in the direction of the arrowssubstantially along the line A—A of FIG. 5(a).

BEST MODE FOR CARRYING OUT THE INVENTION

Mode for carrying out a liquid-drop spraying device of the presentinvention will be described below on the basis of the drawings. FIG. 1shows an example of a liquid-drop spraying device, and is anillustration showing vertical sectional view in center of a liquid-dropdischarge unit. A liquid-drop spraying device has a plurality of unitsranging from a few units to a few hundreds units of a liquid-dropdischarge unit 7 having pressurizing means for discharging a liquid, apressurized room 1 for pressurizing a liquid of discharging, a nozzlefor a liquid discharge 2 connected to the lower portion of thepressurized room 1 and discharging a liquid to the processing portion ofthe liquid-drop spraying device and an inlet hole 10 supplying a liquidinto the pressurized room 1 as one unit corresponding to an aspect ofthe use.

The liquid-drop discharge unit 7 in which a plurality of the pressurizedroom 1 and the pressurized room 1 adjacent each other are connectedthrough a common liquid supplying path 5 via an inlet hole 10 has apiezoelectric\electrostriction element 9 as a pressurizing means in aportion of the upper wall portion of the pressurized room 1. Thepiezoelectric\electrostriction element 9 is consisted of laminating anupper electrode 11, a piezoelectric\electrostriction layer 13 and alower electrode 12, wherein by applying a predetermined voltage signal,the piezoelectric\electrostriction layer 13 is deformed through anelectric field produced between the upper electrode 11 and the lowerelectrode 12, a liquid supplied into the pressurized room 1 is sprayedfrom a nozzle 2 by the pressurizing force produced in the pressurizedroom 1 through deforming the wall portion of the fastened pressurizedroom 1.

Then, the ratio of the pressurized 10 to the nozzle hole 2 (inlet holeaperture/nozzle hole aperture) is made between 0.6-1.6, for example,1.0, and the ratio of the nozzle hole aperture to the nozzle thickness(nozzle hole aperture/nozzle thickness) is made between 0.2-4, forexample, 2. Discharge force and suction force will be well balanced bymaking the ratio of the inlet hole 10 to the nozzle hole 2 within theabove described range, there is no insufficiency of discharge force andsuction force.

It should be noted that it works well with respect to suction whenexceeding over 1.6 but the rate of the pressure escaping to the side ofthe inlet hole at the time of discharge becomes large, resulting ininsufficiency of discharge force. Moreover, when the ratio is smallerthan 0.6, insufficiency of an amount of supplying with respect to anamount of discharge occurs. Furthermore, by making the ratio of thenozzle hole aperture/the nozzle thickness 0.2-4, if the ratio is equalto or less than 4, the residual vibration of liquid level immediatelyafter liquid discharge can be rapidly converged by the contactresistance with the fluid on the wall face of the discharge hole,furthermore, the invasion of bubbles within the pressurized room due tothe pressure variation within the pressurized room during discharge isprevented, the spraying stability can be enhanced, discharge can beperformed in a shorter time period as a result and an amount of sprayingcan be increased, if the ratio is equal to or more than 0.2, since thecontact resistance with the fluid on the wall face of discharge hole,the occurrence of incomplete discharge due to the insufficiency ofdischarge force can be prevented. Moreover, the nozzle hole aperture inthe above described mode for carrying out ranges from 25 μm to 100 μm.

FIG. 2(a) is a graphical representation by passage of time showingvoltage signals applying to the piezoelectric\electrostriction element 9in the case where a liquid-drop is sprayed during charge of thepiezoelectric\electrostriction element. A time T1 is a build-up timethat a liquid is discharged from the nozzle 2 by thepiezoelectric\electrostriction element 9 pressurizing the pressurizedroom 1 through supplying current and charging the piezoelectric body,and a time T2 is a retaining time for retaining final voltage in orderto maintain a state of having completed discharge of a liquid duringcertain time period. A time T3, T4 is a fall time for performing in turndischarges having different time constants, since the initial firstdischarge time constant is larger than the next second discharge timeconstant, the liquid can be flowed into the pressurized room 1 uniformlyfrom a plurality of inlet holes without entrainment of any bubble fromthe side of the nozzle by suctioning the liquid from the inlet hole 10at the slow supplying speed following liquid discharge. Then, since asfor the liquid having started to move, the liquid can be rapidlysuctioned with the second discharge time constant which is smaller one,the liquid supply can be performed smoothly and in a shorter time periodof a driving period time T5 comparing with the case where the liquid issuctioned to the last with the first time constant, thereby enabling astable and a large amount of liquid discharge per unit time period.

FIG. 4 is a graphical representation with measurement data showing theresults of studying the stability of discharge operation of aliquid-drop spraying device by varying voltage so as to migrate adischarge performed with the first discharge time constant to adischarge performed with the second discharge time constant, supposingthat the drive voltage of the piezoelectric\electrostriction element is40 V as being constant and T1=20 μs, T2=5 μs, T3=20 μs and T4=10 μs asbeing constant, FIG. 4(a) shows measurement data, and FIG. 4(b) shows anillustration of the passage of time concerning with applying voltagesignals.

As shown in this Figure, although discharge operation is performed wellin the case where the migration voltage causing discharge with thesecond time constant is between 38% and 63% of final charge voltage,discharge operation is not shown to perform well at 25% and 75% of finalcharge voltage. Thus, there is a range of voltage starting the seconddischarge, it is preferable to start the second discharge with voltageof 35%-70% of applying voltage, i.e., final charge voltage, incompletespraying due to the entrainment of bubbles from the nozzle 2 for theliquid discharge can be prevented and a large amount of spraying can besecured by simultaneously fulfilling the three of the above describedratio of the inlet hole aperture to the nozzle hole aperture, the ratioof the nozzle hole to the nozzle thickness and the second startingdischarge voltage.

It should be noted that a discharge whose discharge time constant islarge, i.e., a suction which is slowly performed occupies most of allsuction steps in the case where the second starting discharge voltage isequal to or less than 35%, although suction itself is securelyperformed, an amount of suction per unit time period is not take large,liquid discharge period cannot be shortened as a result, a large amountof liquid discharge cannot be secured, and if suction time is takensmaller in the situations of the range of the first discharge timeconstant being larger than that of the second discharge time constant soas to take a large amount of suction per unit time period, incompleteliquid discharge will occur because starting of suction is unstable.Moreover, in the case where the second starting discharge voltage isequal to or more than 70%, since the rate of discharge whose dischargetime constant is large, i.e., suction which is slowly performed is toosmall, the starting of suction of the liquid cannot be rapidlyperformed, the entrainment of bubbles within the nozzle for the liquiddischarge will occur and spaying will be unstable by reducing an amountof suction of the liquid from the liquid inlet hole into the liquidpressurized room following the liquid discharge.

Then, it will be good that a time for discharging with the seconddischarge time constant T4 is made ranged from equal to or more than onefourth of specific vibration period T to equal to or less than 20 foldof specific vibration period T at the time the liquid is supplied intothe channel path of structure consisted of the nozzle for liquiddischarge, the pressurized room for pressurizing the liquid dischargedfrom this nozzle, the inlet hole supplying the liquid into the relevantpressurized room and the piezoelectric\electrostriction element makingpressurized room pressurize and operate and the ratio of the initialdischarge time T3 to the second discharge time T4, T3/T4 is made 0.1-20.By defining them in these ranges, liquid supply from the inlet hole canbe smoothly performed with respect to suction speed, and dischargeoperation can be performed quite well without an invasion of any bubblefrom the nozzle hole into the pressurized room. Moreover, specificvibration period in the present invention ranges from 5 μ sec to 40 μsec.

In the case where a time T4 is equal to or less than T\4, since suctionspeed is too high, even if the initial first discharge is performedwell, the liquid supply from the inlet hole performed by suctionoperation during the second discharge is insufficient, and incompletespraying will occur by invasion of bubbles from the nozzle hole into thepressurized room. Moreover, in the case where a time T4 is equal to ormore than 20 T, an amount of suction per unit time period is not takenlarge, the liquid discharge period cannot be shortened as a result, anda large amount of liquid discharge cannot be secured.

Moreover, in the case where the ratio T3/T4 is made equal to or lessthan 0.1, since the rate of initial discharge whose discharge timeconstant is large is smaller, the ratio of liquid suction during theinitial discharge is decreased with respect to the whole amount ofsuction, suction during the second discharge is insufficient in time, ittends to be incomplete spraying, in the case where the ratio T3/T4 ismade equal to or more than 20, since an effect due to the setting of thesecond discharge time constant is lowered, in the viewpoint of a largeamount of spraying, an effect due to the raise of a drive frequency willbe much more effective means.

It should be noted that discharge time constant for the liquid supply ischanged by two steps, however, it is preferable to set discharge timeconstant by more than 2 steps and gradually larger. Moreover, other thana method of deforming the pressurized room by charging thepiezoelectric\electrostriction element for carrying out liquid-dropdischarge, a method of deforming the pressurized room by dischargingfrom the piezoelectric\electrostriction element for carrying outliquid-drop discharge can be performed.

FIG. 3 shows a circuit diagram of a drive electronics supplyingapplication voltage signals of FIG. 2(a), and the presence or absence ofcontrol signal outputted from the drive electronics is shown in FIG.2(b). In CH 1, a charge signal which is an OFF signal when a liquid isdischarged is inputted, in CH 2 upon the initial fall time T3, in CH 3upon the second fall time T4, ON signals are inputted as the firstdischarge signal and the second discharge signal, respectively. In thediagram of FIG. 3, U1A, U1B and U1C are Schmit trigger ICs, R1, R2 andR3 are resistances for use in output current value restriction of Schmittrigger ICs, C11 is a Hi-pass filter for which R101 generates P-MOSdriving waveform, M11 is a charge switch consisted of P-MOS, M12, M13 isthe first and the second discharge switch consisted of N-MOS,respectively, R11 is resistance for time constant setting during charge,R12, R13 are resistants for discharge time constant setting, C_(D) ispiezoelectric body capacity value, and HV is a voltage generated bydirect current source or DC, DC converter.

Then, the charge switch M11 and the resistance R11 form a chargecircuit, the first discharge switch M12 and the resistance R12 form thefirst discharge circuit, the second discharge switch M13 and theresistance R13 form the second discharge circuit. According to these,since time constant of a time T1, T3, T4 of FIG. 2(a) is determined byC_(D)×R11, C_(D)×R12, C_(D)×R13, respectively, when time constantsetting is changed for use in a liquid-drop device, these resistancevalues of R11-R13 are changed, therefore, a drive waveform dischargingin a desired way and at the lower price can be set.

It should be noted that although in the above described mode forcarrying out, a form of discharging liquid-drop during charging thepiezoelectric\electrostriction element is shown, in a form ofdischarging liquid-drop during charge, similar effect can be obtained bymaking circuit constitution of charge circuit and discharge circuit inreverse and providing two switches, the first charge switch and thesecond charge switch, as charge switches.

Moreover, although the above described mode for carrying out is aconstitution of analogue discharge circuit, a drive waveform can bepreferably set by generating a drive waveform with digital signal andconverting it into analogue signal, and Schmit trigger IC can becontrolled well by a microcomputer.

FIG. 5 is an illustration in which a liquid-drop discharge unit fordischarging a liquid-drop is taken concrete shape using MLP (multiplayeractuator) instead of a piezoelectric\electrostriction element bydeforming the pressurized room when discharging contrary to the actionof the above described mode for carrying out, FIG. 5(a) shows a verticalsectional view, FIG. 5(b) shows a sectional view taken in the directionof the arrows substantially along the line A—A. In this Figure, thereference numeral 17 denotes a fixing member for fixing apiezoelectric\electrostriction element, the reference numeral 14denotes+electrode, the reference numeral 15 denotes -electrode, and thereference numeral 16 denotes a piezoelectric\electrostriction element.It should be noted that the same reference numerals are attached to thesame constituting members with those of the above described FIG. 1.

In the case of this form, it will be good that the ratio of the inlethole aperture to the nozzle hole aperture and the ratio of the nozzlehole aperture to the nozzle thickness are made as similar as those ofthe above described mode for carrying out and the second starting chargevoltage is made 30-65% of voltage difference between final dischargevoltage and starting discharge voltage making the final dischargevoltage as a reference. Moreover, it will be good that a time T40 fordischarging with the second discharge time constant is made ranged fromequal to or more than one fourth of the above described specificvibration period T to equal to or less than 20 fold of it and the ratioT30/T40 of the charging time with the initial charge time constant T30to the second charge time constant T40 is made ranged from 0.1 to 20 ina similar manner to the above described mode for carrying out.

In this manner, it is preferable so that a stable liquid discharge canbe performed without producing air bubbles in the liquid of the liquidpressurized room as well as an amount of liquid supply per unit timeperiod is increased, then after discharging liquid-drop, the timeinterval for applying a predetermined voltage signal to thepiezoelectric\electrostriction element without entrainment of bubblesfrom the nozzle can be shortened and an amount of liquid supply can beincreased by making charge time constant large at the time of startingcharge when liquid level vibration in the nozzle for liquid dischargeremains, starting suction of liquid at the rate of slower pressurevariation and consequently rapidly charging with the second charge timeconstant.

What is claimed is:
 1. A method of driving a liquid-drop sprayingdevice, comprising the steps of: providing a liquid-drop spraying devicecomprising a plurality of adjacent liquid-drop discharge units eachhaving a nozzle for discharging liquid, a pressure chamber forpressurizing liquid to be discharged from a respective nozzle, an inlethole for supplying liquid to said pressure chamber and apiezoelectric\electrostriction element to pressurize and operate saidpressure chamber, wherein said inlet holes of each of said liquid-dropdischarge units are connected to a common liquid supply path, andwherein a ratio of an aperture of said inlet hole to an aperture of saidnozzle is in a range of 0.6 to 1.6 and a ratio of said nozzle apertureto a nozzle thickness is in a range of 0.2 to 4; applying apredetermined voltage signal, beginning from a starting charge voltage,to each said piezoelectric\electrostriction element to charge saidpiezoelectric\electrostriction element and deform a wall portion of arespective pressure chamber such that liquid supplied to said respectivepressure chamber is discharged from said nozzle due to the pressureproduced in said respective pressure chamber; holding a final chargingvoltage applied to said piezoelectric\electrostriction element for apredetermined time; sequentially performing first and second dischargingsteps with at least two discharge time constants, wherein an initialdischarge time constant is larger than a second discharge time constant;and starting said second discharging step at a voltage that is 35 to 70%of a voltage difference between said starting charge voltage and saidfinal charge voltage.
 2. The method of claim 1, wherein a time (T4)ranging from a time when a piezoelectric\electrostriction element startsto discharge with the second discharge time constant to a time when saidstarting voltage is again applied to said piezoelectric\electrostrictionelement is in a range of one fourth of a specific vibration period, T,to 20 T when liquid is supplied into a channel path defined by saidnozzle, said pressure chamber and said inlet hole, and a ratio of a time(T3) for discharging with the initial discharge time constant to saidtime (T4) is in a range of 0.1 to
 20. 3. A method of driving aliquid-drop spraying device, comprising the steps of: providing aliquid-drop spraying device comprising a plurality of adjacentliquid-drop discharge units each having a nozzle for discharging liquid,a pressure chamber for pressurizing liquid to be discharged from arespective nozzle, an inlet hole for supplying liquid to said pressurechamber and a piezoelectric\electrostriction element to pressurize andoperate said pressure chamber, wherein said inlet holes of each of saidliquid-drop discharge units are connected to a common liquid supplypath, and wherein a ratio of an aperture of said inlet hole to anaperture of said nozzle is in a range of 0.6 to 1.6 and a ratio of saidnozzle aperture to a nozzle thickness is in a range of 0.2 to 4;discharging current from each said piezoelectric/electrostrictiveelement to deform a wall portion of a respective pressure chamber suchthat liquid supplied to said respective pressure chamber is dischargedfrom said nozzle due to the pressure produced in said respectivepressure chamber; holding a final discharging voltage for apredetermined time; sequentially performing first and second chargingsteps with a least two charge time constants, to reach a final chargingvoltage, wherein an initial charge time constant is larger than a secondcharge time constant; and starting said second charging step at avoltage that is 30 to 65% of a voltage difference between said finalcharging voltage and said final discharging voltage.
 4. The method ofclaim 3, wherein a time (T4) ranging from a time when apiezoelectric/electrostrictive element starts charging with the secondcharge time constant to a time when said piezoelectric/electrostrictiveelement begins to discharge current is in a range of one fourth of aspecific vibration period, T, to 20 T when liquid is supplied into achannel path defined by said nozzle, said pressure chamber and saidinlet hole and a ratio of a time (T3) for charging with the initialcharge time constant to said time (T4) is in a range of 0.1 to 20.